Process of making low-carbon metals or alloys.



UNITED STATES PATENT OFFICE.

FREDERICK M. BECKET, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO ELECTROMETAL- LURGICAL COMPANY, A CORPORATION OF WEST VIRGINIA.

EROCES S OF MAKING LOW-CARBON METALS OR ALLOYS.

Specification of Letters Patent.

Patented June 30, 1908.

Application filed August 24, 1905. Serial No. 275,667.

agara and State of New York, have invented certain new and usefulImprovements in Processes of Making Low-Carbon Metals or Alloys, ofwhich the following is a specification.

This invention is a process for the production of metals and alloys oflow carbon content, and is more particularly applicable to the metalschromium, molybdenum, vanadium and tungsten and to the alloys of thesemetals with iron or nickel.

The invention consists in first producing from a suitable ore an alloyhigh in silicon and low in carbon, and thereafter eliminating all orpart of the silicon by reacting upon further quantities of ore.

As is well known, the presence of carbon is undesirable in the variousmetals and alloys such as ferro-chromium, ferro-tungsten, etc., whichare used for imparting s ecial roperties to steel, and the value of tese a oys increases greatl as their carbon content decreases. Wit theobject of producing metale and alloys of low carbon content manyprocesses have been devised in which reducmg agents other than carbonare employed, such reducing agents being, however, very costl Processeshave also been devised in whio a high carbon alloy is produced andthereafter subjected in a secondary stage to the refining action ofvarious decarburizmg agents which are also either costly or cause largelosses of the metal produced in the first stage.

According to my invention an economlcal process is provided for theproduction of the above mentioned metals and alloys with a' content of.carbon and silicon which may be easil controlled.

I have found that if the oxids or oxygen containing compounds ofchromium, molybdenum, vanadium or tungsten are mixed with varyingquantities of silicious material and subjected to the reducing action ofcarbon, the resulting product containing the metals chromium,molybdenum, vanadium, tungsten or their alloys, contains silicon andcarbon in vary-in proportion, the percentage of carbon being Tower asthe ercentage of silicon is higher; I have also lbund that byincorporating silicious material and carbon in the charge in certainproportions it is possible to produce these metals and alloys containinga very small proportion of carbon. I.

have also found that if the products made in the manner just describedare suitably treated with a new supply of ores or compounds of thedesired metals, the silicon may be practically eliminated and the carboncontent still further diminished.

In order that my invention may be fully understood I shall describe itsapplication to the manufacture of low carbon ferrochro mium, it beingunderstood that this alloy is typical only of those heretoforementioned. As a source of chromium and iron I generally use the mineralchromite containing from 50 to 52 percent. chromium sesquioxid, Cr O andfrom 16 to 17 percent. ferrous oxid, FeO.

With chromite I mix a quantity of sand or.

other silicious material, sufficient carbon to reduce not only the oxideof chromium and of &

iron but also a part or all of the silicious material, and a flux, suchas lime, to form a suitable slag with the impurities generally existingin the chromite and with any portion of the silicious material which maybe unre- (luced. This mixture is then subjected to a hi h tern eratureby means of electrically developed eat and yields an alloy containingchromium, iron, silicon and a small percentage of carbon. This ,is thefirst stage of my rocess. mg the alloy thus produced, preferably inanother electric furnace which when a very 'low carbon product isdesired should have a hearth of material other than carbon, with amixture of chromite or other suitable oxid ore and any fiuxing materialsuch as lime. As a result of this treatment the silicon of the alloyproduced in the first sta e of the process combmes with the oxygen oftained in the chromite or other ore and forms silica which passes intothe slag, an e uivalent proportion of chromium and iron eing reduced andaccumulating with the chromium and iron produced in the first stage. Asone ound of silicon will liberate from the oxid of chromium, Cr O 2.44pounds of chromium, and as this same uantity of silicon will liberatefrom the oxi of iron, FeO, 3.9 pounds of .iron, it will be understoodthat the silicon in the alloy produced in the first stage is replaced bya greater weight of The second stage consists in treat the oxidsconchromium and iron, and that therefore the percentage of carbon in thefinished product may be further reduced.

The roportions of carbon and silica incororated with a given quantity ofchromite to e smelted in the first stage of my process depend upon theuality of the chromite and the ercenta e 0 carbon which it is desiredthe finished erro-chromiumshould contain. To make a ferro-chromiumcontaining about one percent. carbon from chromite of the qtllialityabove referred to, I have found that t e charge may advantageouslyconsist of equal parts by weight of chromite, sand and ordinary coke.The alloy obtained when this charge is smelted in the electric furnacehas approximately the following analysis: chromium 51.3%; iron '17 .5%;silicon 30.0%; carbon 1.2%. In the second stage of the process thisalloy is treated in the electric furnace with a new supply of chromitein the proportion of about six pounds of chromite to every pound ofsilicon in the alloy, this pro ortion of chromite to silicon being veryslig tly in excess of that theoretically necessary to sup ly sufficientoxygen for the conversion of t e silicon to silica. As a result of thistreatment the silicon is practically eliminated, and more chromium andiron have been produced, and the alloy will now analyze practically asfollows: chromium 70.0% iron 28.9%; carbon 1.0%; silicon 0.10%. If analloy of even lower carbon content is required, a higher percenta e of"silicon is obtained in the metallic rmIucts from the first stage of theprocess y using an increased proportion of both sand and coke to chromite, with the result that the carbon content is still lower. Similarlyby using a lower proportion of sand and coke, metallic productscontaining less silicon and more carbon are obtained. It will beseenthat by thus controlling, in the first sta e of the process, the carboncontent of the a oy, the percentage of carbon in the finished productmay be controlled within very narrow limits.

In order to obtain satisfactory results with the metals named it isractically necessary that the first stage of the process should becarried out at the high temperature of the electric furnace, and it'ispreferred that the second or refining stage should also be carried outin the same or other electric furnace. To obtain the advantages ofcontinuous operation and in ener-a1 to conduct the process in the most avantageous manner I prefer to employ two electrlc furnaces in closeproximityto each other, so that the metal or alloy containingconsiderable silicon produced in one-furnace may be ta ped directly intothe other furnace, in whic the second stage of the rocess is carried outand from which the finished roducts are ta ped as desired. By. thismethod the total e ectrical ener consumed in the process is less thanwhen t e metallic products of one furnace are allowed to cool beforetreatment in the same or other furnace.

In the production of chromium, molybdenum, vanadium, tungsten or alloysof these metals in the electric furnace it is known that if sufficientcarbon-is used in the charge to obtain a high yield of these metals fromthe quantity of ore furnaced, the resulting metallic products contain arelatively high proportion of carbon; and as is commonly practiced, ifless than the theoretical quantity of carbon is supplied to the charge,poor yields are obtained and the carbon or graphite in the veryexpensive form of electrodes is rapidly consumed. Referring to the aboveexam le of production of ferro-chromium, ha the silicious material notbeen used in the charge and had the theoretical quantity, 'orslightexcess of carbon, been employed, the carbon in the resulting productWould have been about 8-10 percent. Had considerably less than thetheoretical carbon been used in the charge, the resultingferro-chromium' One of the advantages of my process lies in thepossibility of using almost any excess of carbon as a reducing agent inthe charge employed in the first stage, thereby o taining very highyields of the desired metals and causing a great saving in consumptionof carbon or gra hite electrodes. 4 As a further advantage Ihave foundit possible to produce low carbon, hi h silicon products in an electricfurnace in w 'ch not only the side walls but the hearth on which themetal rests during the first stage of the process are made of the cheapand durable material carbon. As other advantages it may be pointed outthat ores which are usually considered as low grade on account of thepresence'of undue roportions of silica, and which are there- -foreconsidered unfit for the manufacture of the specified metals or alloys,can be successfully and economically used in this process. The sameremark applies to the purity of the carbonaceous reducmg agents such ascoke. When the ores contain sufficient silica for the purpose, no addi'on of silicious material is required, and it is then only necessary toso pro ortion the coke that the desired amount 0 silicon is obtained.This is the case when low carbon ferro-vanadium is producedfiromvanadiferous sandstone.

As the reaction between silicon and the metallic oxids em loyed isstrongly exothermic, a relatively very small amount of electrical energyis required to eliminate the 1 silicon in the second stage of theprocess with the production of a further quantity of the desired metalsalmost equivalent to that theoretically possible wlth a given amount ofsilicon.

The silicon can readily be so far eliminated that the final productchromlte.

I claim:

1. The process of producing low carbon metals or alloys which consistsin producing under electric furnace conditions a metallic product low incarbon and high in silicon, and then oxidizing part or all of thesilicon, substantially as described.

2. The process of roducing low carbon metals or alloys whic consists inreacting under electric furnace conditions with carbon on a chargecontaining an oxid ore and silica to roduqe a metallic productlow incarbon am high in silicon, and then oxidizing part or all of thesilicon, substantially as described.

3. The process of producing low carbon metals or alloys which consistsinproducing under electric furnace conditions a metallic product low incarbon and hi h in silicon and then reacting on said pro uct with anoxid ore to oxidize the silicon, substantially as described.

4. The process of roducing low carbon metals or alloys whic fi consistsin reacting under electric furnace conditions with carbon on a chargecontaining an oxid ore and silica to roduce a metallic product low incarbon and high in silicon and then reacting on said product withadditional quantities of the same oxid ore to oxidize silicon,substantially as described.

5. The process of producing low-carbon ferrochrome, which consists inreacting under electric furnace conditions with carbon on a char econtaining an oxid ore of chromium an silica to produce a metallicproduct low in carbon and high in chromium and silicon, and thenoxidizing part or all of the silicon, substantially as described.

6. The process of producing low-carbon ferrochrome, which consists inreacting under electric furnace conditions with carbon on a chargecontaining an oxid ore of chromium and silica to produce a metallicproduct low in carbon and high in chromium and silicon, and thenreacting on said product with additional uantities of the same oxid oreto oxidize s1 icon, substantially'as described.

In testimony whereof, I affix my signature in presence of two witnesses.

FREDERICK M. BEOKET.

Witnesses JASPER WHITING,

WM. L. HEIM.

